1. Field of the invention
This invention relates to an improvement in thin-film transistor arrays that are used in, for example, colored liquid-crystal display devices, and more particularly, to thin-film silicon transistor arrays with a thin-film structure improved at the intersections of the gate bus lines and the source bus lines.
2. Description of the prior art
As a typical example of conventional thin-film transistor arrays, FIG. 4 shows a thin-film silicon transistor array that is used in a liquid-crystal display panel. In this example, a number of thin-film transistors 1 are arranged in a matrix form to construct a liquid-crystal display device of the active-matrix type. Each thin-film transistor 1 is driven by the input of a scanning signal from the gate bus line 2. With the input of a picture signal from the source bus line 3, the liquid-crystal display panel is operated by the thin-film transistor 1 via the picture-element electrode 4.
In conventional thin-film transistor arrays of this type, intersections X1 of the gate bus lines 2 and the source bus lines 3 have the structure shown in FIGS. 5 to 7. That is, on the top of an insulating substrate 5 made of a glass or the like, there is formed the gate bus line 2 made of tantalum (Ta) with a thickness of 1000 to 4000.ANG.. On the surface of the gate bus line 2, an insulating film 6 made of tantalum oxide (Ta.sub.2 O.sub.5) is formed by anodic oxidation. Then, by plasma chemical vapor deposition, a layered structure is formed which comprises successively a gate insulating film 7 made of SiN.sub.x with a thickness of 1000 to 3000.ANG., an amorphous silicon (a-Si) film 8 with a thickness of 100 to 200.ANG., and a protective insulating film 9 made of SiN.sub.x with a thickness of 1000 to 4000.ANG.. After the deposition of protective insulating film 9 patterning thereof is done by etching. Thereafter, a phosphorus-doped n.sup.+ -type a-Si film 10 with a thickness of 100 to 1000.ANG. is deposited thereon, and the patterning of both the n.sup.+ -type a-Si film 10 and the a-Si film 8 at the same time gives the configuration shown in FIGS. 6 and 7. Moreover, the width of the SiN.sub.x protective insulating film 9 is less than that of the n.sup.+ -type a-Si film 10 and of the a-Si film 8 in both directions in which the gate bus line extends away from the intersection X1, as shown in FIG. 7.
The source bus line 3 and the drain bus line 11 (shown in FIG. 5) are formed on the layered structure mentioned above by the patterning of deposited Ti. The picture-element electrodes 4 are formed by the patterning of a transparent conductive film such as indium-tin-oxide (ITO) after the deposition.
With a liquid-crystal display device using the thin-film silicon transistor array mentioned above, cross talk between the picture elements can be reduced, resulting in a display with a large capacity and high picture quality.
At the present, various devices using a thin-film transistor array such as liquid-crystal display devices and the like are extremely expensive because of the complexity of the panel construction. The structure of the thin-film transistor array itself is as described above, so that it is difficult to reduce the production cost. Thus, the use of a more inexpensive driver to be connected may be considered as one way to reduce the cost of devices using a thin-film transistor array such as liquid-crystal display devices and the like.
However, in the intersection X1 of the source bus line 3 and the gate bus line 2 mentioned above for the conventional thin-film transistor arrays, the electric capacity is formed by the gate bus line 2, the insulating films 6, the gate insulating film 7, and the a-Si film 8; because this electric capacity is relatively large, the drive load becomes large. Therefore, it is necessary to connect a source driver and gate driver with large driving capacity, which makes it difficult to use inexpensive drivers.